Field of the Invention
The invention relates to a circuit configuration having at least one nanoelectronic component and a method for fabricating the component.
In order to produce a circuit configuration with an ever higher packing density, dimensions of a component of the circuit configuration will probably measure just a few nanometers in the very foreseeable future. An example of such a so-called nanoelectronic component is a single-electron component in which circuit operations are realized by individual electrons. C. D. Chen et al., xe2x80x9cAluminium single-electron nonvolatile floating gate memory cellxe2x80x9d, Appl. Phys. Lett. 71 (14) (1997) 2038 describes a single-electron transistor which is essentially produced from aluminum.
Nanoelectronic components may also be biological nerve cells or molecular-electronic structures (see e.g. C. M. Fischer et al., xe2x80x9cOrganic Quantum Wells: Molecular Rectification and Single-Electron Tunnellingxe2x80x9d, Europhys. Lett. 28, 129 (1994)).
In general, nanoelectronic components are proposed which are fabricated using a very different technology from conventional CMOS components.
F. G. Pikus et al., xe2x80x9cNanoscale field-effect transistors: An ultimate size analysisxe2x80x9d, Appl. Phys. Lett. 71 (25) (1997) 3661, investigate a nanoelectronic CMOS component.
K. Yano et al., xe2x80x9cA Room-Temperature Single-Electron Memory Device Using Fine-Grain Polycrystalline Siliconxe2x80x9d, IEDM (1993) 541, disclose a nanoelectronic memory cell including a transistor. Source, drain and channel regions of the transistor are produced by patterning an amorphous silicon layer having a thickness of 4 nm. Grains of the silicon layer have horizontal dimensions of approximately 10 nm. The channel region and a gate electrode of the transistor are surrounded by SiO2. If the transistor is operated with low current, then a narrow channel forms in the channel region, which channel includes a chain of grains between which individual electrons tunnel. The threshold voltage of the transistor can be changed analogously to an EEPROM, which corresponds to programming of the memory cell. In order to program e.g. a logic 1, the voltage at the gate electrode, which acts as control gate electrode, is increased to an extent such that electrons hop to grains of the channel region which lie outside the channel, and remain there. The charged grains act analogously to a floating gate electrode of the EEPROM, so that the threshold voltage of the transistor is altered.
It is accordingly an object of the invention to provide a circuit configuration having at least one nanoelectronic component and a method for fabricating the circuit configuration which overcomes disadvantageous of the prior art apparatus and methods of this general type.
With the foregoing and other objects in view there is provided, in accordance with the invention a circuit configuration having at least one nanoelectronic component, in which the circuit configuration includes: a semiconductor substrate; and a CMOS circuit that is configured in the semiconductor substrate. The CMOS circuit includes at least one CMOS component. An insulating layer is configured on the semiconductor substrate and covers the CMOS component. A first nanoelectronic component is configured above the insulating layer. Conductive structures are configured in the insulating layer. At least one of the conductive structures connect the first nanoelectronic component to the CMOS component. A plurality of nano-switching blocks are configured above the insulating layer. Each one of the plurality of the nano-switching blocks are defined by a group of further nanoelectric components. Each one of the plurality of the nano-switching blocks has lines with RC times that interconnect the further nanoelectric components of the one of the plurality of the nano-switching blocks. Each one of the plurality of the nano-switching blocks has a size such that the RC times of the lines are not greater than 1 ns. A first drive circuit for the plurality of the nano-switching blocks is provided in which the first drive circuit is defined by the CMOS circuit. A plurality of second drive circuits is provided. Each one of the plurality of the nano-switching blocks is adjoined by a respective one of the plurality of the second drive circuits that is connected between the one of the plurality of the nano-switching blocks and the CMOS circuit. The conductive structures connect the CMOS circuit to the plurality of the second drive circuits. One of the plurality of the second drive circuits combines the lines of the one of the plurality of the nano-switching blocks such that a number of the conductive structures that are connected to the one of the second drive circuits is less than a number of the lines of the one of the plurality of the nano-switching blocks.
With the foregoing and other objects in view there is provided, in accordance with the invention a method for fabricating a circuit configuration, which includes steps of: providing a semiconductor substrate; using a CMOS method to produce at least one CMOS component in the semiconductor substrate; after producing the CMOS component, applying an insulating layer on the semiconductor substrate and covering the CMOS component with the insulating layer; producing a conductive structure in the insulating layer and connecting the conductive structure to the CMOS component; and using a nano-pattering technique to produce a nanoelectronic component above the insulating layer such that the nanoelectronic component is connected to the CMOS component by the conductive structure.
The circuit configuration has a high packing density since the CMOS component is configured under the nanoelectronic component.
The invention enables the integration of nanoelectronic components into microelectronic products.
Since the nanoelectronic component is not produced until after the CMOS component has been produced, it is not attacked by the method steps for producing the CMOS component. The nano-patterning technique may differ from the conventional CMOS methods.
In accordance with an added feature of the invention, the circuit configuration may include further nanoelectronic components. In order to increase the packing density, the nanoelectronic components are configured as close together as possible. For a given number of nanoelectronic components which are interconnected by lines, the dense configuration causes the lines to be shortened. This is advantageous since resistances of the lines are reduced. On the one hand, this means a smaller energy loss in the circuit configuration. On the other hand, the product of the resistance and the capacitance of the lines, the so-called RC time, is likewise small, so that changes in the voltages of the lines take place more quickly, and the circuit configuration switches more quickly.
In order to realize short lines despite a large number of nanoelectronic components, it is advantageous to group the nanoelectronic components into nano-switching blocks. A nano-switching block is a configuration of adjacent nanoelectronic components which are interconnected by lines having nanomete-wide cross sections. Although the grouping increases the number of lines of the circuit configuration, by the same token the lines are shorter. Furthermore, the grouping facilitates the dissipation of heat from the circuit configuration.
In accordance with an additional feature of the invention, the nano-switching blocks are each so small that the RC times of their lines are not longer than 1 ns. Using the conductive structure and further conductive structures configured in the insulating layer, the nano-switching blocks are connected to a CMOS circuit, which includes the CMOS component. Preferably, each nano-switching block is connected to the CMOS circuit through at least one of the conductive structures. A further advantage of the invention is manifested here: since the CMOS circuit is configured under the nano-switching blocks, and not beside them, for example, the conductive structures do not run in the two-dimensional plane in which the nano-switching blocks are configured, but rather run, at least partly, perpendicularly to the plane. Consequently, the conductive structures have more space, so that the nano-switching blocks can be configured at small distances from one another, which leads to a greater packing density. It may be important, precisely when grouping the nanoelectronic components into a plurality of nano-switching blocks, for the conductive structures to be provided with a great deal of space. This is because a large number of small nano-switching blocks generally require a larger number of conductive structures than a large nano-switching block, since each of the nano-switching blocks is separately connected to the CMOS circuit.
The CMOS circuit may be, for example, a first drive circuit for the nano-switching blocks.
In accordance with another feature of the invention, a plurality of second drive circuits are provided. In order to reduce the number of conductive structures which are connected to the nano-switching blocks, it is advantageous to configure, adjoining each nano-switching block, a second drive circuit which is connected between the nano-switching block and the first drive circuit. The second drive circuit combines the lines in the nano-switching block in such a way that the number of conductive structures connected to the second drive circuit is less than the number of lines. The conductive structures connect the first drive circuit to the second drive circuits. Such a hierarchical construction reduces the density of the conductive structures, so that the CMOS circuit can be produced in unstrained dimensions. The second drive circuit can be produced e.g. using the nano-patterning technique used to produce the nano-switching blocks.
In accordance with a further feature of the invention, the nano-switching blocks may be memory cell configurations, for example. A memory cell may be configured for example like a memory cell in accordance with C. D. Chen et al. (see above). The second drive circuit includes single-electron transistors, for example. The second drive circuit may, for example, combine bit lines of the nano-switching block in such a way that signals of the bit lines are forwarded sequentially to the first drive circuit. The first drive circuit determines which of the nano-switching blocks is addressed.
In accordance with another added feature of the invention, in order to connect CMOS components of the CMOS circuit to one another and to the nano-switching blocks, one or more metallization planes may be configured in the first insulating layer, the metallization planes being part of the conductive structures. Contacts, which are likewise parts of the conductive structures, are configured in the insulating layer and connect the first drive circuit to the metallization plane or the metallization plane to the second drive circuits.
In accordance with another additional feature of the invention, the metallization plane can be produced by first applying a lower part of the insulating layer. First contacts, which adjoin the CMOS circuit, are produced in the lower part of the insulating layer. The metallization plane is produced on the lower part of the insulating layer by conductive material being applied and patterned. An upper part of the insulating layer is subsequently applied. Second contacts, which adjoin the metallization plane, are produced in the upper part of the insulating layer. The nano-switching blocks are produced in such a way that they are connected to the second contacts.
In accordance with yet an added feature of the invention, the insulating layer can be applied in more than two parts, so that a plurality of contacts and a plurality of metallization planes can be produced.
In accordance with yet an additional feature of the invention, a part of the lines of the nano-switching block may be part of nano-metallization plane configured in the insulating structure. A nano-metallization plane is a metallization plane whose lines and contacts have dimensions of a few nanometers. The provision of such a metallization plane enables the crossing of the lines of the nano-switching block.
In accordance with yet another feature of the invention, in order to produce the nanoelectronic component, a layer may be applied on the insulating layer and patterned. The layer contains e.g. aluminum and is processed, as explained in C. D. Chen (see above).
In accordance with yet a further feature of the invention, the layer may also include titanium or niobium. In this case, the nanoelectronic component may be produced by partly oxidizing the layer with the aid of a scanning atomic force microscope, as is explained e.g. in K. Matsumoto, xe2x80x9cSTM/AFM Nano-Oxidation Process to Room-Temperature-Operated Single-Electron Transistor and Other Devicesxe2x80x9d, Proc. IEEE 85, 612 (1997).
The construction of the nanoelectronic component is irrelevant to the invention. Thus, the nanoelectronic component may be e.g. a biological nerve cell, a molecular-electronic structure e.g. in accordance with C. M. Fischer et al. (see above), a CMOS component in accordance with F. G. Pikus et al. (see above) or a memory cell in accordance with K. Yano et al. (see above).
In accordance with a concomitant feature of the invention, the nanoelectronic component may have grains of conductive material which are enclosed by insulating material. Individual electrons can tunnel from grain to grain.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a circuit configuration having at least one nanoelectronic component and method for fabricating the component, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.